It's my understanding that they got rid of the Costumes because nobody was buying them.
I found this especially annoying since they removed them the day before I got paid, and the first thing on my list to buy was the Imperial Assault cruiser skin. Now if I want it, I have to waste vast resources on a useless vessel from a system I despise...
The day will not save them. And we own the night.
I buyed almost all of them, except the Prometheus costume.. that was ugly, anyway, they could be available now, there is more ways to have Zen now than before F2P, or as reputation projects, if they don't want to sell them..